Wire forming manufacturing allows the rapid creation of custom parts by shaping wire feed stock often having diameters of about 0.25 inches, though wire forming is practiced over a wide range of wire diameters. When wire formed components are joined together, typically by spot welding, relatively strong and lightweight frames may be created. Wire formed structures have found widespread acceptance throughout the automotive industry due to the strength, weight, and resiliency of these parts.
Joining wire formed components to flat metal parts has not presented substantial difficulties for the wire forming industry. The wire may in some cases be welded to the flat component or even more advantageously might pass through an aperture in the flat component, in which case electric current may be applied to the wire on each side of the aperture thereby heating the end of the wire that has proceeded through the aperture to a plastic state. When heated, the metal wire may be deformed against the flat part to form a hot upset weld. Hot upset forging or welding is a well known technique for enlarging elongated work pieces at selected points and is described generally in Bachmann, U.S. Pat. No. 3,396,567.
Although the ability to join formed wire to flat metal pieces is desirable and necessary, in many instances it is preferable to join wire formed pieces to metal tubing. Hollow metal tubing generally provides a greater strength to weight benefit than solid flat metal pieces. Traditionally, wire formed parts have either been welded to metal tubes or mounted in brackets welded to the metal tubes, however, the spot welding processes typically used have required relatively long cycle times, have not produced sufficiently uniform welds, and have resulted in defects and rattles because of weld splatter and weld slag. Prior attempts to utilize resistance heating and upset forging techniques when joining wire forms to tubing have not been successful because the entire segment of wire passing through the hollow tube as well as the end portion extending from the tube have been heated to a plastic state. Attempts to upset the portion of the wire extending through the tubing have generally resulted in simply creating a mass of metal within the tube.